Procedure for etching of materials at the surface with focussed electron beam induced chemical reactions at said surface

ABSTRACT

The invention refers to a procedure for etching of materials at the surface by focussed electron beam induced chemical reactions at said surface. The invention is characterized in that in a vacuum atmosphere the material which is to be etched is irradiated with at least one beam of molecules, at least one beam of photons and at least one beam of electrons, whereby the irradiated material and the molecules of the beam of molecules are excited in a way that a chemical reaction predetermined by said material and said molecules composition takes place and forms a reaction product and said reaction product is removed from the material surface-irradiation and removal step.

This application is a continuation of Ser. No. 10/428,269 filed May 2,2003 now U.S. Pat. No. 7,238,294 and claims priority thereto.Application Ser. No. 10/428,269 claims priority to EP Patent No.02010233.1 filed May 16, 2002.

The invention relates to a procedure for etching of materials at thesurface with focussed electron beam induced chemical reactions at saidsurface according to the features of the introductory part of claim 1.In general the invention relates to focussed electron beam inducedchemical reactions and their application to material processing. Inparticular it relates to the removal of material with high spatialresolution using electron beam induced etching. It also relates to therepair of photo masks and the modification of integrated circuits andother devices on a nanometer scale.

A number of direct writing technologies, most of them based on focussedparticle or photon beams, have been developed that they allow themodification of materials on a nanometer scale. Examples where thosetechnologies are applied in the semiconductor industry include therepair of photo masks and the modification of integrated circuits. Inmost of these applications it is required that the technology can removeas well as add material with sub-micrometer precision For materialaddition it might be necessary to deposit several materials havingspecific chemical and physical properties.

For material removal it might be required to remove one materialselectively from a combination of materials without creating damage inthe remaining material. Other requirements might include the obtainablepositioning accuracy and the minimum feature size, e.g. resolution, ofthe process. Some of those requirements will be illustrated in thefollowing for photolithographic mask repair, which is one preferredapplication of the present invention.

For this purposes photon beam ablation, photon beam induced chemicaletching, ion beam sputtering and ion beam assisted chemical etching areor could potentially be used to etch materials used for photo masks inthe semiconductor fabrication process.

Photolithographic masks usually consist of a light transparentsubstrate, e.g. glass, quartz, which carries a structured chromium metallayer of 100 nm thickness. On the masks certain areas are patternedusing a light absorbing material—absorber—, such as chromium, to blocklight transmission in these areas. These masks are used in thesemiconductor industry to project a pattern located on the mask onto awafer, which is covered with a light sensitive substance, e.g.photoresist. These masks can have at least two kinds of defects, whichneed to be repaired.

1) Absorber material is missing, where there should be absorber—cleardefect—and

-   -   2) absorber material in areas where there should be no        absorber—opaque defect.

Currently, common mask repair tools are based on a laser beam or afocussed ion beam—FIB. Chemical and/or physical processes that are orcould be employed by these tools are photon beam ablation, photon beaminduced chemical etching, ion beam sputtering and ion beam assistedchemical reactions, deposition and etching.

It is state of the art to remove absorber material such as chrome by afocussed laser beam. Usually, high energy, short pulse laser beams areused. Interaction between the laser beam and the material can be forexample photothermal or photochemical. For mask repair laser ablation isused, where the material is evaporated by locally heating it with thelaser beam. Laser induced chemical reactions could potentially also beused for mask repair, where the laser beam provides the energy to causea reaction between the material and a suitable gas such as chlorine,resulting in volatile products that desorbs. In this context it isreferred to the article “MARS: Femtosecond laser mask advanced repairsystem in manufacturing” of R. Haight, D. Hayden, P. Longo, T. Neary andA. Wagner in Japanese Vacuum Science Technology, 17(6), Nov./Dec. 1999,pages 3137 to 3143 and to the Article “A review of laser-microchemicalprocessing” of D. J. Ehrlich and J. Y. Tsao, J. Vac. Sci. Technol. B 1(4), Oct-Dec 1983.

However, all photon beam based processing suffers from a limitedresolution due to the Abbé diffraction resolution criterion, which tellsthat the obtainable resolution is ca. 0.5 times the wavelength of thelight in use.

Ion beam sputtering is an effective process with potentially 10 nmresolution, but generates damage in the substrate which is not tolerablefor several applications. Ion beam assisted chemical etching is also aneffective process with somewhat lower resolution, approximately 100 nm,but also generates damage in the substrate which is not tolerable forseveral applications. Both processes are applied for etching of opaquedefects in photo mask repair.

With the increasing resolution requirements of photo masks for the chipproduction in the next generations, and with the additional technicalmodification of the mask pattern to obtain the required resolution suchas optical proximity effect structures or phase shift masks, andEUV-multilayer masks, the semiconductor industry is today in thesituation that the approved methods of laser ablation and deposition, aswell as the ion beam sputtering, and chemically assisted ion beametching and deposition is no longer tolerable because of lack ofresolution and lack of transmission of the substrate after the repair.Therefore, a nondestructive soft and clean chemical etching method needsto be applied for opaque defects in photomasks and “next generationmasks” such as EUV masks, which does not implant metal ions into thesubstrate and does not mix the underlying material causing structuraldamage introduced by the ion impact.

Currently, focussed electron beams are only used to repair clear defectsby locally adding absorber material. This is done by exposing a selectedlocal area with an electron beam, while simultaneously delivering a flowof precursor gas to the area. The electron beam then decomposes theprecursor gas, e.g. hydrocarbons, inorganic, or organometallicmolecules, leaving behind a deposit in the area that was scanned by theelectron beam. Removal of material is more difficult because electronsdo not deliver enough momentum to eject, e.g. sputter, substrate atoms,like a focussed ion beam can. At present, electron beam etching has onlybeen demonstrated for a few material systems, where activated by thefocussed electron beam, a chemical reaction is induced, which results involatile products and, thus, a removal of material.

Although there is only very little research on electron beam inducedetching reactions, the reaction will certainly be a complex sequence ofsingle elementary reactions, which will involve several steps such asadsorption of precursor gas molecules—physisorption and/orchemisorption—, diffusion of precursor molecules or their fragments intothe substrate, one or more reactions between these precursor moleculesand the substrate atoms and finally the desorption of the reactionproduct. In order to confine the etching process to an area that hasbeen exposed with a focussed electron beam and thus provides the highspatial resolution of the process, it is required that the etchingprocess does not occur spontaneously and at least one step in thereaction sequence has to be induced by electron beam exposure. Anexample for electron beam induced etching is the removal of silicondioxide —SiO₂— with XeF₂ where etching only takes places in areas thathave been simultaneously exposed to a beam of electrons and XeF₂molecules. See for example: Ted Liang, A. Stivers, G. Liu, G. Dao, V.Liberman, M. Rothschild, S. T. Palmacci and L. Scipioni, “Damage-freeMask Repair Using Electron Beam Induced Chemical Reactions”, 2nd Int'l.Symp.on 157 nm Lithography, Dana Point, Calif. (May 2001).

The very high resolution and precision of material etching in the photomask repair and circuit editing procedures of the semiconductor industryin its novel circuits and masks with structures below the wavelength ofthe ultra violet light requires a novel technology to be employed forthe repair of such structures.

Therefore, it is an object of the present invention to improve theprocedure for etching of materials at the surface with focussed electronbeam induced chemical reactions at said surface so as to overcome thecited drawbacks and to propose a procedure for locally removing materialwith higher spatial resolution.

It is especially an object of the invention to etch multilayerstructures without mixing of the layers of the metals and insulatorswhich can have thicknesses in the range of several tens of nanometers.

This object is achieved by the characterizing features as defined inclaim 1 in conjunction with the features in its introductory part.

The understanding underlying the invention is that a combination of afocussed beam of electrons, a beam of molecules and a beam of photonsprovides the high spatial resolution and the required activation energyfor a chemical reaction, forming a reaction product which can beremoved. Hereby said reaction only takes place in areas that have beenexposed and chemically or physically modified by said beam of electrons.

According to the invention the procedure comprises the following steps:

in a vacuum atmosphere the material which is to be etched is irradiatedby at least one beam of molecules, at least one beam of photons and atleast one beam of electrons, whereby the irradiated material and themolecules of the beam of molecules are excited in a way that a chemicalreaction predetermined by said material and said molecules compositiontakes place and forms a reaction product and said reaction product isremoved from the material surface—irradiation and removal step.

Especially, the chemical reaction sequence between the material to beetched and the gas of the beam of molecules contains at least oneelemental chemical or physical reaction which is induced selectively byelectron beam exposure. In addition, at least one elemental chemical orphysical reaction in the reaction sequence, is induced or enhanced bysaid beam of photons with a well specified energy and duration to inducesaid chemical reaction and gettering said reaction product in saidirradiation and removal step.

On the one hand, the energy delivered by said beam of photons could bephoto thermal, especially to raise the surface temperature of thematerial to be etched locally and temporarily by a defined amount ascontrol by the laser intensity and wavelength.

On the other hand, the energy delivered by said beam of photons couldcause a photo chemical reaction, especially whereby the wavelength ofthe laser light is tuned to a wavelength to cause resonant electronicexcitation in the material or within an intermediate chemical speciesgenerated by previous electron beam exposure.

Especially, said elemental reaction induced by the photon beam could bethe evaporation of the reaction products from the surface by said pulsedand focussed beam of photons, which heats the material locally to atemperature above the vaporization temperature of the reaction product.

Said beam of photons is delivered by a continuous laser source such as asemiconductor diode laser with a wave-length from IR to visible—2000 nmto 250 nm—or by a pulsed laser system such as an eximer laser or a ionlaser with a wavelength from 2000 nm to 157 nm.

Especially, in the irradiation and removal step the beam of electrons isdelivered with a scanning focussed electron beam system with a spot sizeof 0.1 to 1000 nm to generate a dense distribution of adsorptions sitesfor the reaction partner molecules from the beam of molecules.

Said beam of molecules consisting of one or more gases could be issuedfrom a gas feeding system in a stoichiometric composition to thematerials surface during said irradiation and removal step.

According to one embodiment of the invention initially the surface ofthe material to be etched is cleaned—cleaning step.

Advantageously, the cleaning step is realized by a chemical reaction toremove contamination, oxides or other material covering the surface. Onthe one hand, in the case that the material covering the surface layeris formed by carbon contamination the chemical reaction forming afurther reaction product is initiated by an additional beam of moleculescomprising water, hydrogenperoxyde, chlorine or other halogen compoundswhich release excited oxygen and/or halogen atoms to react with thecarbon of the surface layer.

Additionally or alternatively, the cleaning step is realized by heatingand subsequent evaporation of the surface of the area to be cleaned witha focussed beam of photons of sufficient energy density to heat thesurface to a temperature above the vaporization temperature of thefurther reaction product.

-   -   According to one embodiment of the invention, the beam of        molecules comprises different precursor gases.

Advantageously, the gas feeding system is formed by a multi jet systemwith a flow rate from 0,1 to 10000 monolayers/sec.

For instance, at least one of the precursor gases delivered by themulti-jet gas delivery system, consists of molecules, which are notreactive spontaneously or when exposed to a beam of photons, but can beactivated by electron beam exposure.

Furthermore, the precursor gases could contain halogens, which releasesaid halogen when exposed to said beam of electrons in a process knownas dissociative electron attachment.

According to one embodiment of the invention, said beam of molecules,said beam of photons and said beam of electrons are either deliveredsimultaneously or delivered subsequently, in a synchronized and timelycontrolled fashion with defined delivery times and delays between thevarious exposures.

In the case that said beams are delivered subsequently, the cycle ofexposures is repeated until a desired etch depth has been reached. Therepetition loop time can be controlled by exposing adjacent or otherpixels in a timely sequence as required to generate a defined time lagbefore the start of the next exposure sequence, or by turning theelectron beam off, e.g. beam blanking, for a defined period of time.

In this connection there are the following possibilities:

On the one hand, a defined dose of said beam of molecules beam “A” isdelivered first, followed by an exposure of said beam of electrons,followed by a defined dose of said beam of molecules “B”.

On the other hand, a defined dose of a said beam of molecules “A” isdelivered first, followed by a pulse of said beam of photons of definedduration, intensity and wavelength, followed by a defined dose of saidbeam of molecules “B”.

According to one embodiment of the invention, the material to be etchedcould be chromium. Then the beam of molecules contains halogens such asXeF₂, Cl₂, Br₂ or I₂—halogen beam. Furthermore, the beam of moleculescould contain oxygen such as O₂, H₂O or H₂O₂—oxygen beam—and is used inaddition to said halogen beam. The halogen and oxygen containing beamsare delivered simultaneously. Or, if they are delivered subsequently,said beam of molecules “A” is a halogen beam and said beam of molecules“B” is an oxygen beam or said beam of molecules “A” is an oxygen beamand said beam of molecules “B” is a halogen beam.

In summary, the present invention describes a method to remove materialwith high spatial resolution using a focussed electron beam to definethe area to be removed. The material is removed by a reaction betweenthe substrate material and a suitable precursor gas such as halogens.The reaction results in volatile compound that desorbs from the surface.A combination of focussed electron beam and a laser beam is used toinitiate a reaction sequence starting with the adsorption of precursormolecules and ending with the desorption of the reaction products.Within the reaction sequence the electron beam induces one or morereaction steps and provides the spatial resolution of the process. Thelaser beam delivers the required activation energy for one or morereaction steps that cannot be activated by the electron beam alone.However, the laser beam induced reaction takes place only in areas thathave been exposed and “activated” or altered by the electron beam.

Further advantages and features of the invention will become apparentfrom the following description of an embodiment with reference to theattached drawing in which

FIG. 1 is a schematic view of a mask repairs system according to theinvention;

FIG. 2 is a schematic view of the main step of the procedure, namelyirradiation and removal step, and

FIG. 3 is a schematic view of subsequent beams of electrons, photons andmolecules according to the invention.

FIG. 1 shows a schematic set up of a mask repair system 10 having aknown molecular beam delivery system, referred to in the following asgas supply system 12, a known electron beam system 14, a known photonbeam system, referred to in the following as laser beam system 16, and acomputer control system 18 for timely triggered action and cooperationof these beams—beam of molecules, beam of photons and beam ofelectrons—for the procedure according to the invention.

The gas supply system 12 comprises a reservoir 20 for liquid or solidprecursors—Peltier cooled—, feedings 22 of gaseous precursors, a feedingof pressurized air 24, a valve control 26, a pressure gauge 28 and atemperature control 30 for the reservoirs 20. The valve control 26, thepressure gauge 28 and the temperature gauge are connected forcontrolling via a CAN open bus 32 to the computer control system 18.

The reservoirs 20 are connected via feedings 34 having nozzles 36 to anozzle-manifold 38. Also, the feedings 22 having nozzles 36 areconnected to the nozzle manifold 38. The nozzle-manifold 38 has endvalves 40 at each nozzle. Nozzles 36 are connected with the valvecontrol 26 for operating the valves in the feedings 22 and 34 withpressurized air.

The electron beam system 14 comprises an electron beam control unit 42.

The laser beam system 16 comprises a laser power supply 44 and a laserunit 46 and a trigger unit 72. The laser unit works together with amirror 48 to deflect the laser beam 50 on the mask 52 to be repaired.Alternatively, the laser beam can be focussed and directed onto the maskby using a optical fibre system connected to a focussing lens systeminside the vacuum chamber, not shown.

The electron beam control unit 42 comprises a Faradays cage 54 forcurrent measurement and a secondary electron detector 56 andcorresponding control units 68 and 70, as well as beam deflection coils76 and a beam blanker.

An environmental chamber 58 is provided wherein the procedure accordingto the invention described below takes place. This can also be achieved(resembled) by using an electron beam system, which enables to operatethe sample chamber at high pressure using a variable pressure orenvironmental vacuum pressure control system, as supplied by instrumentbuilders. Those systems also allow to rise the pressure in the samplechamber up to 15 torr without disabling the operation of the electronbeam. The gas supply system 12, the electron beam system 14 and thelaser beam system 16 act in the environmental chamber 58. Aninterferometer controlled motorized stage 59 is provided to position themask 52.

The computer control system 18 comprises four windows for the control ofthe mask repair system 10, namely a multijet window 60, an electron beamwindow 62, a repair control window 64 and a microscope window 66.Furthermore, a beam control computer 68 is provided to control theelectron beam unit 42. Therefore, the electron beam computer unit 60 isconnected with the Faradays cage for current measurement and a beamcontrol 70 is connected with the electron beam unit 42 in the known art.

For the time dependent control a trigger 72 is provided which isconnected with the beam control 70 and the laser power supply 44.

Furthermore, a laser interferometer stage control unit 74 is connectedwith the stage 59 and the computer control system 18.

The procedure with the mask repair system 10 is now described:

The electron beam of a high resolution scanning beam system is used,which employs the brightest and in long terms stable electron source,the thermal field emission cathode. Well developed electron opticalsystems allow to focus the electron beam to 2 nm spot diameters havingenergies from 100 eV up to 40 keV or even 200 kev The distribution ofthe electrons in the crossover of the beam is very sharp defined, due tothe low lens aberrations and the low energy width of the electron sourceand the specialized beam path, which in some cases has no crossover(where the energy width of the beam broadens by Coulomb interaction ofthe electrons). In principle electron beam systems achieve a betterperformance, in terms of resolution and power density, than ion beam orphoton beam systems by almost an order of magnitude each.

Electron beams surpass the ion beams in power density by orders ofmagnitude, however, due to the low momentum transfer of electrons to theatoms of the workpiece, a much higher number of electrons is requiredthan ions for the same action. Typically 50 to 250 times more electronsare required in comparison to ions. This results also from the muchhigher scattering cross sections of the slow ions, which are 48 timesthe square root of the mass number of the ion slower than the electrons,and therefore interact better with the atoms. In addition the Coulombinteraction for knock on processes is stronger by the factor of thenuclear charge of the ions. The ion impact however, generates a cascadeof focussed knock on processes, which transfer the momentum of the ioninto the depth of the sample, where it damages the material. The ionitself is implanted in a shallow region close to the surface of thesample and acts as an impurity and absorbs deep UV photons, especiallyat 157 nm.

A clean and nondestructive method is to use absorption of chemicals, toactivate the absorbed chemicals to react with the substrate metal toform a solid, liquid or gaseous compound, and in the case of a liquid orsolid reaction product to drive these molecules off the surface with afine focussed high power laser pulse, which thermally heats the surfaceto a temperature above the sublimation or evaporation temperature of thechemical compound.

The procedure according to the invention employs the gas supply system12 with high gas flux switching capability as described in DE 100 42 098A1 and WO 02/19575 A1. These documents are part of the disclosure ofthis application in connection with the invention. This allows thedeposition of single monolayers of precursors at the workpiece surface.A scanning electron beam system like a scanning electron microscope or alithography system is required to pattern the surface of the workpiecewith a well defined dwell time and current density.

The process of additive nanolithography is well described in thearticle: H. W. P. Koops, J. Kretz, M. Rodolph, M. Weber, G. Dahm, and K.Lee, “Characterization and application of materials grown by electronbeam induced deposition”, Jpn. J. Appl. Phys Vol. 33 (1994) 7099-7107.This article is part of the disclosure of this application in connectionwith the invention.

The beam of electrons might cause a potentially reactive molecule, forexample halogens, to chemisorbs onto the target material or it mightchange the chemical composition in some other way under electron beaminduced activation, while no chemisorption or alterations in compositionoccur in areas that are not exposed to the electron beam.

In any case the effect of the local electron beam exposure will be thatthe exposed area is in some chemically activated state, that whenselectively induced by a laser beam, by for example photo-thermal orphoto-chemical activation, those areas will further react causing anetching process of the target material, see FIG. 2. In order to providethe activation energy and prevent spontaneous reaction in areas notexposed by the electron beam the laser wavelength and light intensitymight need to be adjusted to selectively cause a reaction only inelectron beam modified areas. The laser light can be applied during thewhole process, or after the end of an electron beam exposure cycle.

One of the novel features of the procedure according to the invention isthe timely coupling of the pulsed laser photon beam, which is switchedon to stimulate chemical reactions of the adsorbed chemicals with thesubstrate surface before or after a electron beam induced reaction hastaken place. This interlock requires a specialized trigger and laserpulse emission of the light to the sample.

In this “layer by layer etching” scheme the electron beam would bescanned or rastered across the area just long enough to cause a chemicalmodification of one or a few monolayers at the surface. A short laserpulse will then selectively desorb this modified layer for examplethermally—this is known in the literature as laser induced thermaldesorption—or photochemically by causing an electronic excitation ofmolecules, which are only present in the modified layer. The cycle ofelectron beam exposure and laser pulse is then repeated until thematerial is removed to the desired depth, see FIG. 3.

Possible events and actions used in the present invention are listed intable 1. In the following the concept of the present invention isillustrated using the etching of chromium, a commonly used absorbermaterial on photolithographic masks, as an example. However, it shouldbe understood that the described process including the nature and orderof the described steps as well as the chemicals used are forillustration purposes only and does not limit the scope of the presentinvention to this particular process.

Before starting the etching process the chromium surface is cleaned byapplying a short laser pulse to heat the surface. Alternatively or incombination with the laser pulse a suitable gas, for example water vaporand electron beam exposure can be used to clean the surface from organiccontamination.

In the first step of the etching cycle the surface is exposed to asuitable precursor gas such as halogens, alone or in combination withoxygen or water vapor. If more than one gas is needed, for example Cl₂and O₂, those gases can be delivered simultaneously or separately in aprecisely controlled order and duration.

In the second step the area to be removed is exposed with an electronbeam, which causes a reaction between the adsorbed precursor gas and thechromium substrate.

Alternatively, instead of delivering elemental halogens in step 1, anon-reactive gas such as a fluoro- or chlorocarbons might be used. Thosecompounds are known to decompose under electron beam exposure in aprocess known as dissociative electron attachment, whereby halogens arereleased. Since this process is selectively induced only by electronsone can achieve adsorption of released halogens on the target materialonly in areas that have been exposed by an electron beam.

In the third step the reaction product, for example nonvolatilechromiumoxychloride, is desorbed by heating the surface with a laserbeam. For some etch chemistries the laser light might be applied duringthe whole process to locally raise the temperature above the desorptiontemperature of the reaction products. However, it is preferred to applya short laser pulse at the end of an electron beam exposure cycle. Inthis “layer by layer etching” scheme the electron beam would be rasteredacross the area just long enough to cause a chemical modification of oneor a few monolayers at the surface. A short laser pulse will thenselectively desorb this modified layer for example thermally, this isknow in the literature as laser induced thermal desorption, orphotochemically, by causing an electronic excitation of molecules, whichare only present in the modified layer. The cycle of precursor gasadsorption, electron beam exposure and laser pulse is then repeateduntil the material is removed to the desired depth.

The endpoint of the etching is determined chemically, if there is achemical selectivity in etching the metal but not the quartz substrate.In this case the removal of material will stop once the quartz surfaceis reached. This endpoint can also be detected from the changingsecondary electron or back scattered electron emission at the etchedlocation. Alternatively, the desorbed monolayers material during theetch process can be monitored with a mass spectrometer in DC or a lockin method, since the desorption and evaporation takes place in welldefined time intervals. The detection of the endpoint of the etchingprocess can also be done evaluating spectroscopically the light emittedfrom the substrate and the chemical reaction products which is generatedby electron and/or laser beam induced luminescence.

Table 1 shows schematic steps of the etching procedure

Action Beam Result Photon beam IR to Visible Desorption of on to heatadsorbates Sample the sample cleaning Electron Areal scan to ex-Generation of ad- beam 100 eV cite adsorption sorption sites for to 200keV sites chemicals Multi-Jet gas Gas or precursor Adsorption of re-mixture on mixture for action partners with 1 to 1000 stoichiometric andinstant Monolayers/sec composition of reaction etch gas ElectronActivation of Chemical etching beam 100 eV precursors and to solid,liquid to 200 keV chemical etching or gaseous reaction compound Photonbeam Pulsed high power Evaporation of the UV to IR laser triggeredchemical etch with the electron product beam Repetition Multilayer bymul- of the trig- tilayer ablation gered action of the surface. of thedif- ferent beams

In summary, the present invention is intended for the etching ofmaterials where electron beam exposure alone is not sufficient to inducea full reaction sequence. In those cases it is assumed that in additionto one or more elementary reaction steps, which can be activated byelectron beam exposure, there are one or more reaction steps, which donot proceed at a sufficient rate at room temperature. In this cases abeam of photons, preferably from a laser source, is used to provide theadditional activation energy. The interaction between the photons andthe material can be either photo-thermal, e.g. local heating of thesubstrate, or photo-chemical, e.g. the photon beam induces resonantelectronic transitions to activate a intermediate reaction product.

To preserve the required spatial resolution provided by the focussedelectron beam writing it is required that at least one step in thereaction sequence is activated by the electron beam. The effect of theelectron beam exposure will be that the exposed area is in somechemically activated state, that when selectively induced by a laserbeam those areas will further modified causing an etching process of thetarget material. In order to provide the activation energy and preventspontaneous reaction in areas not exposed by the electron beam the laserwavelength and light intensity might need to be adjusted to selectivelycause a reaction only in electron beam modified areas.

In the preferred embodiment of the invention the beam of electrons andthe beam of photons exposure as well as the exposure to one or more beamof molecules can be either simultaneous or in a controlled sequence withdefined exposure time and delays between different exposures, see FIG.3. This flexibility allows to tailor the process to the specific needsof the material to be etched and the precursor chemicals. Some of thesteps that might be involved in the etching process are listed in theabove-mentioned table 1.

List of Reference Signs 10 mask repair system 12 molecular beamsystem/gas supply system 14 electron beam system 16 photon beamsystem/laser beam system 18 computer control system 20 reservoirs forliquid or solid precursors 22 feedings of gaseous precursors 24 feedingof pressurized air 26 valve control 28 pressure gauge 30 temperaturecontrol 32 CAN open bus 34 feedings 36 nozzles 38 manifold nozzle 40 endvalve 42 electron beam unit 44 laser power supply 46 laser unit 48mirror 50 laser beam 52 mask to be repaired 54 Faradays cage 56secondary electron detector 58 environmental chamber 59 interferometercontrolled motorized stage 60 multijet window 62 electron beam window 64repair control window 66 microscope window 68 beam control computer 70beam control 72 trigger 74 Laser interferometer stage control 76Electron beam deflector coils and beam blanker

1. Procedure for etching of materials at the surface by focussedelectron beam induced chemical reactions at said surface, characterizedin that in a vacuum atmosphere the material which is to be etched isirradiated with at least one beam of molecules, at least one beam ofphotons and at least one beam of electrons, whereby the irradiatedmaterial and the molecules of the beam of molecules are excited in a waythat a chemical reaction predetermined by said material and saidmolecules' composition takes place and forms a reaction product and saidreaction product is removed from the material surface.
 2. Procedureaccording to claim 1, characterized in that said beam of photons isdelivered by a laser source, said laser source is a pulsed laser system.3. Procedure according to claim 1, characterized in that said beam ofmolecules is a beam of gas and said chemical reaction between saidmaterial to be etched and said gas of said beam of molecules includes atleast one elemental chemical or physical reaction which is inducedselectively by an electron beam exposure.
 4. Procedure according toclaim 1, characterized in that said reaction product is evaporated fromthe surface by said photon beam pulsed and focussed, which heats thematerial locally to a temperature above the vaporization temperature ofsaid reaction product.
 5. Procedure according to claim 1, characterizedin that a laser delivers said beam of photons, said beam of photons isphoto thermal to raise the surface temperature of the material to beetched locally and temporarily, and controlling said temperature of saidmaterial by selecting a laser intensity and wavelength.
 6. Procedureaccording to claim 1, characterized in that a laser delivers said beamof photons and causes a photo chemical reaction, said laser is tuned tocause resonant electronic excitation in said material or within achemical species generated by said previous electron beam exposure. 7.Procedure according to claim 1, characterized in that a cycle ofexposures is repeated until a desired etch depth has been reached. 8.Procedure according to claim 1, characterized in that a defined dose ofa beam of molecules selected from the group consisting of a halogen beamand an oxygen beam is delivered first, followed by an exposure of saidbeam of electrons, followed by a defined dose of a third beam which isselected from a group consisting of a halogen beam and an oxygen beamnot used immediately prior to the application of the beam of electrons.9. Procedure according to claim 1, characterized in that initially saidsurface of said material to be etched is cleaned.
 10. Procedureaccording to claim 9, characterized in that said surface of saidmaterial is cleaned by a chemical reaction to remove contamination,oxides or other material on said surface of said material.
 11. Procedureaccording to claim 9, characterized in that carbon contamination on saidsurface of said material is cleaned by a chemical reaction wherein afurther reaction product is initiated by an additional beam of moleculescomprising water, hydrogen peroxide, or chlorine or other halogencompounds which release excited halogen atoms to react with said carboncontamination on said surface.
 12. Procedure according to claim 1,characterized in that said beam of molecules comprises differentprecursor gases.
 13. Procedure according to claim 12, characterized inthat a multi-jet gas delivery system is utilized and in that a gasfeeding system is formed, said gas feeding system includes saidmulti-jet system with a flow rate from 0.1 to 10000 monolayers/sec. 14.Procedure according to claim 12, characterized in that a multi-jet gasdelivery system is utilized and in that at least one of said precursorgases, necessary for removal of said reaction product is delivered bysaid multi-jet gas delivery system, said at least one of said precursorgases includes molecules which are not reactive spontaneously or whenexposed to said beam of photons but can be activated by said beam ofelectrons.
 15. Procedure according to claim 1, characterized in that inorder to facilitate irradiation of said material and removal of saidreaction product the beam of electrons is delivered with a scanningfocussed electron beam system with a spot size of 0.1 to 1000 nm togenerate a dense distribution of adsorption sites.
 16. Procedureaccording to claim 15, characterized in that a gas feeding system isutilized and that said beam of molecules comprises selected chemicalcompounds in a stoichiometric composition issued from said gas feedingsystem to said surface of said material.
 17. Procedure according toclaim 16, characterized in that said beam of selected chemical compoundsin a stoichiometric composition issued from said gas feeding system areexcited by said beam of photons with a well specified energy andduration to induce a chemical reaction to produce said reaction product.18. Procedure for etching of materials at the surface by focussedelectron beam induced chemical reactions at said surface, characterizedin that in a vacuum atmosphere the material which is to be etched isirradiated with at least one beam of molecules, at least one beam ofphotons, and at least one beam of electrons, said beam of molecules,said beam of photons and said beam of electrons are deliveredsimultaneously whereby said irradiated material and said molecules areexcited in a way that a chemical reaction predetermined by said materialand said molecules' composition takes place and forms a reaction productand said reaction product is removed from said material surface. 19.Procedure according to claim 18, characterized in that said beam ofphotons is delivered by a laser source, said laser source is a pulsedlaser system.